The invention relates to a measuring circuit of the D.C. component of the current flowing through the primary winding of the output transformer of an inverter.
In power converter inverters, the existence of interference D.C. currents in the primary winding of the inverter output transformer gives rise to transformer saturation problems.
Up to now, the use of transformers comprising an air gap, and consequently able to withstand the flow of a D.C. component, enabled this problem to be overlooked. The increasingly frequent use of transformers without an air gap however makes this problem a more and more crucial one. It is therefore desirable to eliminate this D.C. component, and to accomplish this, it is necessary to have a measurement of it which can be used by the inverter control circuit to automatically reduce this component to zero.
As the A.C. component, at mains frequency, has a large amplitude in comparison with the D.C. component, the use of RC filters would lead to a considerable phase displacement which would unbalance the feed-back loop designed to achieve automatic control.